There's no way I can post it in full here without everyone having stupidly wide monitors. Click above pic to visit my dA where the full version can be downloaded (4910x768, 1MB)

I made use of the sunlight while it was here today. Set the 50D to high speed continuous, stuck the 100-400L on the front fully extended and started my arm workout.

Settings for this was Tv mode at 1/800s and -2/3EV as the Gulls tend to white out against the background. Lens on IS mode 2 although I'm not sure if that was needed at all given the shutter speed. If I could do it again, I would go to -1 EV and knock the shutter down to 1/1000 as I still lost some highlights and I think that's motion blur on the wingtips.

That's NICE, Popo! Looking good!
Have you tried to do that with Highlight Priority? It could help you keeping the highlights on the gull at the cost of a little detail lose in the background. It may be worthy

If I understand highlight priority correctly, all it does is underexpose and compensate for the brightness, which is effectively what I'm doing semi-manually...

It underexposes selectively. It's like the Shadows/Highlights tool in PSE. Tweaking the shadows slider will lighten the shadows but will leave midtones and highlights alone. Darkening highlights will affect only highlights.

It has to underexpose everything, as the sensor would be set as a whole. In the software part the selective adjustment made to bring the exposure back to nominal for mapping. As cautioned in the manual, this may result in a loss of shadow detail.

I did play with the highlight priority setting a little another time, but don't use it now. It wont let you select high ISO settings while it is active.

Also, in PSE turning up the lighten shadows slider can darken the shadows too! But the only times I've seen that have been in bright low contrast images. They might be better calling the function shadow correction as opposed to simple lightening. Note this is only the shadow slider, with no contribution from the highlight slider at all.